Passive roll stabilizers

ABSTRACT

The invention includes a passive roll stabilizer for floating bodies having a tendency to roll about a roll axis of the body, the stabilizer comprising an elongated tank lying across the roll axis of the body, internal end surfaces of the tank bounding volumes at either end of the tank for containing stabilizing fluid, restriction means arranged in the tank to control movement of fluid lengthwise of the tank between said volumes, at least one surface of said restriction means sloping transversly of the tank, and at least one other surface of the stabilizer extending lengthwise of the tank and cooperating with said sloping surface to define an upwardly widening flow passage in a central length of the tank, the restriction means and said volumes at the ends of the tank being substantially symmetrically arranged about a vertical plane containing the roll axis of the body when the stabilizer is in the static (horizontal) condition.

United States Patent [72) Inventor Richard James Jacob 3,347,199 10/1967 Goodrich et al. 114/125 Brighton, Sussex, England 3,407,772 10/1968 Goodrich 114/125 [2]] A 802506 Primary Examiner-Trygve M. Blix [22] Filed Feb. 26,1969 A C K k & S n [45] Patented June 8, 1971 Omey amemn er am u on [73] Assignee National Research Development f g s d ABSTRACT: The invention includes a passive roll stabilizer [32] P 2: 5 for floating bodies having a tendency to roll about a roll axis of y the body, the stabilizer comprising an elongated tank lying [3]] 3 n across the roll axis of the body, internal end surfaces of the tank bounding volumes at either end of the tank for containing stabilizing fluid, restriction means arranged in the tank to con- [54] PASSIVE ROLL STABILIZERS trol movement of fluid lengthwise of the tank between said 10 Claims 12 Drawing Figs volumes, at least one surface of said restriction means sloping transversly of the tank, and at least one other surface of the [52] U.S.Cl 114/125 stabmzer amending lengthwise f the tank and cooperating [5 H '3'- Cl B63) 43/06 with said sloping surface to define an upwardly widening flow [50} Field of Search 114/125 passage in a eel-ma} langth f the tank, the restriction means [56] Reerences Cited and saidyolumes at the ends of the tank being substantially symmetrically arranged about a vertical plane containing the UNITED STATES PATENTS roll 'axis of the body when the stabilizer is in the static 3,272,170 9/1966 Dreyfus 1 14/125 (horizontal) condition.

1\ I i i J l 24- z 4 l L 26" f T 3 H6 Ti? 11? i t m /6 l Z0 29 -32 22 25 Y2 PATENTED JUN 8 197:

SHEET 2 [1F 3 PATENTEDJUN 8l97| 3583353 SHEET 3 UF 3 PASSIVE ROLL STABILIZERS This invention relates to passive roll stabilizers for ships or other floating bodies.

According to the present invention, a passive roll stabilizer for ships or other floating bodies includes an elongated tank adapted to contain fluid and lying across the roll axis of the body, and restriction means so arranged in the tank to control movement of fluid lengthwise of the tank that in the static (horizontal) condition of the stabilizer, the tank and fluid extend substantially symmetrically on each side of a vertical plane containing or adjacent to the roll axis of the body, whereas during a rolling motion of the body, fluid in the tank moves lengthwise of the tank along an upwardly widening flow passage extending in a central length of the tank and bounded in part by a sloping surface provided by the restriction means thereby to generate on the body a moment opposing the rolling motion.

The restriction means conveniently presents two distinct end faces spaced apart along the length of the tank and joined by said sloping surface. These end faces are preferably of similar shape to one another and may incline towards one another with their base edges lying parallel to the roll axis of the floating body.

Additionally, the distinct end faces may be of similar sub stantially triangular shape in which case the sloping surface above referred to is of substantially rectangular or trapezium shape.

The restriction means in the embodiments above described may also have the feature of being symmetrical about a plane containing the highest part of the restriction means and extending perpendicularly to the roll axis of the body thereby to present two upwardly widening flow passages in said central length of the tank.

In a further embodiment, the restriction means presents only two surfaces and these are each of similar triangular shape with a common edge located in or near a plane containing the roll axis of the body.

In one form of the above-described embodiments, the base of the restriction means is spaced from the tank floor surface. Alternatively or additionally edges of the restriction means leading to the highest part thereof, may be contained in a sidewall of the tank.

If desired, the restriction means may extend only partially across the tank between the two sidewalls of the tank, the bottom surface(s) of the flow passage(s) then being provided by the floor surface of the tank.

The base portion of the restriction means preferably extends over about the middle two-fourths of the tank length.

The tank conveniently contains an amount of stabilizing fluid to a depth such that with the stabilizer in its static (horizontal) condition the height of the restriction means is about two-thirds of the maximum depth of fluid in the tank. Typically in this case, the fluid will extend about half way up the height of the tank when the stabilizer is in its static (horizontal) condition, but the invention also extends to the case where the fluid level in the tank is not greater than the maximum height of the restriction means.

It is pointed out here that for a given depth of fluid in the stabilizer tank, any passive roll stabilizer is able to give its optimum performance under only one particular set of sea and loading conditions. Admittedly, the stabilizers can be "retuned" to suit other sets of operating conditions by varying the amount of fluid in the tank, but such a solution presents its own problems. It is for example very difficult, when rolling is taking place, to assess the amount of fluid actually present in the tank so that there is little information available at the time for deciding just how the fluid depth should be varied. Moreover, tuning adjustments of this kind always involve a certain amount of care and as a consequence there is always the risk that a wrong adjustment might be made which could actually encourage the rolling motion of the body instead of deterring it. Hence, especially where, for example, the sea and loading conditions of the body are not expected to vary signifcantly, the compromise solution is usually accepted of maintaining the fluid depth in the tank at that value which would give an optimum performance for the average or most usual sea and loading expected. With known passive roll stabilizers, this compromise solution results in a considerable loss of stabilizer efficiency when other than the average or most usual operating conditions exist.

A stabilizer in accordance with the present invention on the other hand, promises a more acceptable all round performance in that its optimum performance is less critically dependent on the depth of fluid in the tank and on the degree of tuning than has been the case with the known types of passive roll stabilizer.

In order that the invention may be more fully understood, embodiments thereof will now be described, by way of example, with reference to the accompanying somewhat diagrammatic drawings of which:

FIG. I is a plan view ofa first embodiment of the invention;

FIG. 2 is a section taken on the centerline II-Il of FIG. 1;

FIG. 3 is a section taken on the line lll-III of FIG. 1;

FIG. 4 is a plan view of a second embodiment of the invention;

FIG. 5 is a section taken on the centerline A-A of FIG. 4;

FIG. 6 is a plan view of a modification of the first embodi ment of the invention;

FIG. 7 is a plan view of a modification of the second embodiment of the invention with the top of the tank broken away more clearly to show the position of the restriction in the tank fluid;

FIG. 8 is a plan view of a third embodiment of the invention with the top of the tank broken away more clearly to show the position of the restriction in the tank fluid; and

FIGS. 9 to 12 are sections taken on the centerlines of modifications or further modifications of the embodiments illustrated in FIGS. 1 to 8.

Thus referring first to FIGS. 1 to 3, a passive roll stabilizer in accordance with the present invention includes a tank 10 having a floor surface 12 of a rectangular boundary and four sidewalls I4, 16, I8, 20. The two sidewalls l4 and I8 extend upwardly of the floor surface 12 and have inside surfaces lying substantially perpendicular to the roll axis A-A of the ship or other floating body (not shown) in which the stabilizer is located. A restriction 22 extends across the tank between the walls 14 and 18. The restriction has two end surfaces 24, 25 of similar triangular shape the base edges 26 of these surfaces being contained in the floor surface 12 and the side edges 28, 29 being of a same length as each other. As indicated in FIG. 3, these end surfaces 24, 25 incline towards one another at an angle of about l45 to the end regions 30, 31 of the floor surface 12. The two end surfaces 24, 25 of the restriction are joined by two side surfaces 32, 33 of trapezium shape. The surfaces 32, 33 extend between corresponding sides of the triangular surfaces 24, 25 and slope continuously upwards from the base of the restriction to a common edge 34 joining the apices of surfaces 24, 25, thereby to define between end portions 35, 36 of the tank 10, two upwardly widening flow passages 37 (FIG. 2).

As indicated in FIGS. 1 to 3 the restriction 22 extends over about the middle two-fourths of the floor surface 12. In operation the tank 10 contains an amount of stabilizing fluid 38, e.g., water or oil, such that with the stabilizing fluid in its static condition and the floor surface 12 disposed horizontally, the height h] of the edge 34 is about two-thirds of the height h3 of the fluid in the tank. Typically too, the height h3 of the fluid is about half the height h2 of the tank itself. It will be appreciated in this respect that FIGS. 1 to 3 illustrate a situation in the stabilizer which can only exist when the body containing the stabilizer is floating in absolutely calm water so that no rolling occurs.

When more usual conditions prevail, however, the body will be rolling about the roll axis A-A (FIG. I).

Thus, in operation, rolling of the body about axis A-A in say, an anticlockwise sense as viewed in FIG. 3, will cause part of the fluid 38 originally located in end portion 36 to move up over the adjacent inclined end surface 25 and edges 28 into passages 37 whilst stabilizing fluid originally located in the passages 37 will flow over edges 29 into the other end portion 35. The stabilizing fluid thus transferred to the left-hand side of the tank (as viewed in FIG. 3) will oppose subsequent rolling of the body in the opposite (clockwise) sense, thereby imposing a degree of roll stabilization on the body. A similar degree of roll stabilization is obtained during the subsequent anticlockwise roll of the body, stabilizing fluid which has followed the clockwise roll of the ship now being located principally at the right-hand end of the tank (as viewed in FIG. 3) so as to oppose the subsequent lifting of that end during the anticlockwise roll of the body.

In a second embodiment of the invention (FIGS. 4 and 5), the restriction 39 has a single side surface 32 and this side surface is of rectangular shape. The end faces 24, 25 of the restriction are each of a substantially right-angled triangle shape with the hypotenuse edge lying in the floor surface 12 of the tank 10. The slopes of the surfaces 24, 25 and 32 are such as to give the restriction 39 a height h4 (FIG. 5) at the tank wall 14 about equal to the height hl of the previous restriction.

The operation of this last-described stabilizer and of those hereafter described, will be evident from the description relating the first embodiment of the invention. Hence this operation will not be further discussed here, it being understood that elements or parts of elements common to the various embodiments, or performing identical or similar functions in the various embodiments, have been indicated throughout by the same terminology, and where appropriate and convenient, also by the same reference numerals.

The present invention also includes the two embodiments above described modified to present two flow channels instead of one, or vice versa. According to another feature the restriction need not extend wholly across the tank between the sidewalls l4 and 18 so that the or each upwardly widening flow passage has a bottom surface provided by the floor of the tank. The modification shown in FIG. 6 of the first described embodiment illustrates both these features. Thus, in this modification the restriction 42 is essentially one half" (in the direction A-A) of the restriction 22 of the first embodiment (as cut along the line III-III in FIG. 1) except that the slopes of the trapezium surface 32 and of the end (triangular) surfaces 24, 25 are changed to give the restriction a height at the tank wall 14 about equal to the height hl ofthe previous restriction 22, and the bottom longitudinal edge 44 of the restriction is spaced from the tank wall 18 in order that the bottom surface of the upwardly widening flow passage 37 be provided by the floor surface 12 of the tank 10.

In accordance with another feature of the invention, the fluid level in the tank need not be greater than the height of the restriction, and the modification of the second embodiment shown in FIG. 7 illustrates the case where the highest part 46 of the restriction 48 is an edge lying in the surface of the tank fluid when the stabilizer is in its static (horizontal) condition. It will be noted that the restriction 39 shown in FIG. 4 is essentially one half (in the direction A-A) of the restriction 48 of the modification shown in FIGS. 6 in exactly the same sense that the restriction 42 of the modification shown in FIG. 6 is essentially one half" (in the direction A-A) of the restriction 22 of the embodiment shown in FIG. i.

In a third embodiment (FIG. 8) of the invention, the upper part 49 ofthe restriction 50 projects above the fluid surface 51 in the tank with its uppermost part 52 located in the tank wall 14. The restriction has only two surfaces 53, 54 and these are each of similar triangular shape with a common edge 55 located in or near the fore and aft center plane of the stabilizer, i.e., in or near the plane A-A containing the roll axis of the body. The other edges 56,57 of the triangular surfaces are contained in the sidewall 14 of the tank and in the tank floor surface 12 respectively. For a same sized tank as the tank 10, the slopes of the two surfaces 53, 54 are such that the uppermost part 52 of the restriction is at a height of about hl (FIG. 2) above the tank floor surface.

Although the embodiments of FIGS. 7 and 8 have been illustrated with fluid levels equal to or less than the height of the restriction, it will be appreciated that they will also function satisfactorily with the restriction wholly immersed in the stabilizing fluid. In this latter case the stabilizers may be substantially identical in sections taken along their centerlines to those illustrated in FIGS. 2 and S. The converse is also true, i.e., the embodiments of FIGS. 1 to 6 could also be made to work satisfactorily with the fluid levels reduced to a height equal to or less than the height of the restrictions in those embodiments.

It will of course be understood that where the body having the stabilizer is intended for travel, e.g., a ship as opposed to a floating rid, it is immaterial, in the cases where the stabilizer restriction is not symmetrically disposed between the walls 14, 13 of the tank, whether the tank wall adjacent the topmost part of the restriction is made the leading wall rather than the trailing wall of the tank, or vice versa.

FIGS. 9 and 10 show sections taken on the centerlines of the embodiment of FIG. 6 and of modifications of the embodiments illustrated in and/or described with reference to FIGS. l to S, 7 and 8 in which the longitudinal edge (s) of the restriction is/are spaced from the adjacent tank wall (s) in order that the bottom surface of the upwardly widening flow passage (s) 37 be provided by the floor surface 12 of the tank 10.

Alternative forms of the various embodiments above described and of their modifications and variations above described, are shown in FIGS. 11 and 12 in which the restriction is spaced from the floor of the tank on support pillars 60 so that stabilizing fluid can also flow underneath the restriction.

It will be appreciated that although FIGS. 9 to 12 show the restriction wholly immersed in the fluid when the stabilizer is in its static (horizontal) conditions, the top surface of the fluid may be lowered if desired so that the highest part of the restriction is in or above the surface of the fluid in this condition.

One important advantage of those embodiments in which the restriction is spaced from the tank floor or having the sloping triangular ends of the restriction extending upwardly right from the floor surface of the tank is that transfer of fluid from one end of the tank to the other is facilitated even at moderate angles of roll and trapping of fluid in the wing parts of the tank is avoided.

Another advantage of all the illustrated embodiments is that having the end surfaces of the restriction triangular and sloping precludes excessive turbulence in the fluid flow over these ends whilst the sloping nature of the or each triangular, trapezium shaped or rectangular side surface (s) of the restriction allows it to act as an elementary beach, so that movement of the stabilizing fluid in the tank as induced by pitching of the body will be more readily decayed.

Another important advantage of the stabilizer of the present invention is that it is relatively easy to construct and maintain since easy access is afforded merely by removing the base of the tank in the vicinity of the restriction. This advantage is of course not present when the restriction is spaced from the tank floor.

By way of example, a passive roll stabilizer having the characteristics of that illustrated in FIGS. 1 to 3 of the drawing and suitable for a ship of average size, might include a tank 10 of a dimension of about 65 feet extending from side to side of the ship, and a dimension of about l0 feet in a direction longitudinally of the ship, i.e., in the direction A-A. The restriction would then conveniently be about 32 feet wide at the base and arranged symmetrically over the centerline of the ship. The triangular end surfaces of the restriction would subtend an angle of about to the end regions of the floor surface 12 of the tank (as above mentioned), and the height of the restriction edge 34 would be about 2 feet, 3 inches above the surface 12. The stabilizing fluid would have (in the horizontal static condition) a maximum depth in the tank of about 3 feet. If, as in the illustrated embodiments, and as is usual with passive roll stabilizers, a closed tank is used the top surface of the tank must not interfere significantly with the action of the stabilizing fluid if the efficiency of the stabilizer is not to be impaired. Hence with the dimensions above given a tank height of about 6 feet 6 inches would be suitable.

Further embodiments of the present invention will readily occur to those skilled in the art.

Thus, the invention includes passive roll stabilizers, for example, in which the restriction means comprises an upper portion similar in shape to the restrictions above described as having bases extending across the full width of the tank, and comprises a lower portion wholly extending across the full width of the tank below, and integral with, the upper portion, thereby to present with the upper portion end faces of the restriction means sloping upwardly towards one another. With this modification, service ducts for the floating vessel can be passed lengthwise of the vessel through the lower portion of the restriction means without in any way interfering with the operation of the stabilizer.

The invention also extends to passive roll stabilizers in which the restriction means comprises two or more restrictions each similar in shape to those above described in the various embodiments but separated from one another transversely of the tank so that the upwardly widening flow passage has its bottom part located in or provided by the floor surface of the tank and its side surfaces provided by sloping surfaces of the restrictions. Additionally, or alternatively, these restrictions might be separated lengthwise of the tank so that the central plan (A-A) of the tank need not necessarily pass through any part of the restriction means.

it will also be understood that the invention is not limited to the use of oil or water as the stabilizing fluid but extends to the case where other fluids are used. The tank fluid could, for example, equally well be a suspension of heavy solids in a liquid.

lclaim:

l. A passive roll stabilizer for floating bodies having a tendency to roll about a roll axis of the body, the stabilizer comprising an elongated tank lying across the roll axis of the body, internal end surfaces of the tank bounding volumes at either end of the tank for containing stabilizing fluid, restriction means arranged in the tank to control movement of fluid lengthwise of the tank between said volumes, at least one surface of said restriction means sloping transversely of the tank,

and at least one other surface of the stabilizer extending lengthwise of the tank and cooperating with said sloping surface to define an upwardly widening flow passage in a central length of the tank, the restriction means and said volumes at the ends of the tank being substantially symmetrically arranged about a vertical plane containing the roll axis of the body when the stabilizer is in the static (horizontal) condition.

2. A stabilizer as claimed in claim 1 wherein the restriction means presents two distinct end faces spaced apart along the length of the tank andjoined by said sloping surface.

3. A stabilizer as claimed in claim 2 wherein the end faces are of similar shape one to the other and incline towards one another with their base edges lying parallel to the roll axis of the floating body.-

4. A stabilizer as claimed in claim 2 wherein the distinct end faces are of similar substantially triangular shape and the sloping surface is ofa substantially rectangular shape.

5. A stabilizer as claimed in claim 2 wherein the distinct end faces are of similar substantially triangular shape and the sloping surface is ofa substantially trapezium shape.

6. A stabilizer as claimed in claim 1 wherein the restriction means is symmetrical about a plane containing the highest part of the restriction means and extending perpendicularly to the roll axis of the body, said restriction means thereby presenting two surfaces sloopin transversely of the tank and cooperating with two of sa| 0t er surfaces of the stabilizer to present two upwardly widening flow passages in said central length of the tank.

7. A stabilizer as claimed in claim 1 wherein the restriction means presents only two surfaces and these are each of similar triangular shape with a common edge located in or near a plane containing the roll axis of the body.

8. A stabilizer as claimed in claim 1 comprising support means for the restriction means whereby the base of the restriction means is spaced from the tank floor surface.

9, A stabilizer as claimed in claim 1 wherein the restriction means extend only partially across the tank between the two sidewalls of the tank, the bottom surface(s) of the flow passage(s) then being provided by the floor surface of the tank.

10. A stabilizer as claimed in claim 1 wherein the base portion of the restriction extends over about the middle twofourths of the tank length, the tank contains an amount of stabilizing fluid to a depth such that with the stabilizer in its static (horizontal) condition the height of the restriction is about two-thirds of the maximum depth of fluid in the tank, and the fluid extends about half way up the height of the tank. 

1. A passive roll stabilizer for floating bodies having a tendency to roll about a roll axis of the body, the stabilizer comprising an elongated tank lying across the roll axis of the body, internal end surfaces of the tank bounding volumes at either end of the tank for containing stabilizing fluid, restriction means arranged in the tank to control movement of fluid lengthwise of the tank between said volumes, at least one surface of said restriction means sloping transversely of the tank, and at least one other surface of the stabilizer extending lengthwise of the tank and cooperating with said sloping surface to define an upwardly widening flow passage in a central length of the tank, the restriction means and said volumes at the ends of the tank being substantially symmetrically arranged about a vertical plane containing the roll axis of the body when the stabilizer is in the static (horizontal) condition.
 2. A stabilizer as claimed in claim 1 wherein the restriction means presents two distinct end faces spaced apart along the length of the tank and joined by said sloping surface.
 3. A stabilizer as claimed in claim 2 wherein the end faces are of similar shape one to the other and incline towards one another with their base edges lying parallel to the roll axis of the floating body.
 4. A stabilizer as claimed in claim 2 wherein the distinct end faces are of similar substantially triangular shape and the sloping surface is of a substantially rectangular shape.
 5. A stabilizer as claimed in claim 2 wherein the distinct end faces are of similar substantially triangular shape and the sloping surface is of a substantially trapezium shape.
 6. A stabilizer as claimed in claim 1 wherein the restriction means is symmetrical about a plane containing the highest part of the restriction means and extending perpendicularly to the roll axis of the body, said restriction means thereby presenting two surfaces sloping transversely of the tank and cooperating with two of said other surfaces of the stabilizer to present two upwardly widening flow passages in said central length of the tank.
 7. A stabilizer as claimed in claim 1 wherein the restriction means presents only two surfaces and these are each of similar triangular shape with a common edge located in or near a plane containing the roll axis of the body.
 8. A stabilizer as claimed in claim 1 comprising support means for the restriction means whereby the base of the restriction means is spaced from the tank floor surface.
 9. A stabilizer as claimed in claim 1 wherein the restriction means extend only partially across the tank between the two sidewalls of the tank, the bottom surface(s) of the flow passage(s) then being provided by the floor surface of the tank.
 10. A stabilizer as claimed in claim 1 wherein the base portion of the restriction extends over about the middle two-fourths of the tank length, the tank contains an amount of stabilizing fluid to a depth such that with the stabilizer in its static (horizontal) condition the height of the restriction is about two-thirds of the maximum depth of fluid in the tank, and the fluid extends about half way up the height of the tank. 